Earth's Inner Core
　　Scientists have long struggled to understand what lies at the planet's center, Direct observation of its center is impossible，so researchers must_____（51）to other evidence．
　　In 1889，a German scientist detected a severe earthquake in Japan．Geophysicists concluded that shock waves_____（52）jolts（晃动）from one side of Earth through the center to the other side．Then in 1936，Danish geophysicist Inge Lehmann studied the waves______（53） to determine that within Earth's core of molten（熔化了的）iron lies a solid inner core-but_____ （54）that core was made of eluded（难倒）her．Other geophysicists quickly determined that Lehmann's inner core was composed mostly_____（55）iron. Since then，Lehmann's discovery has_____（56）conventional Earth science．
　　But now scientists are challenging traditional theory with new and radical _____（57） For example，Earth's center could actually contain an“inner core within the inner core，claim Ishii and colleague Adam Dziewonski．Analyzing hundreds of thousands of earthquake wave _____（58）,they maintain that the inner core has at its heart a tiny, even more solid sphere（球体） . This sphere''may be the oldest fossil____（59）from the formation of Earth，”says Dziewonski．Dziewonski and Ishii speculate that shortly_____（60） Earth formed around 4.8billion years ago，a giant asteroid（小行星）smashed into the young planet and nearly melted it. But Earth's center didn't quite melt；it______（61）mass as the planet cooled. The core within a core may be the kernel（核心）that endured．“Its presence could change our basic ideas about the_____ （62）of the planet，”Dziewonski says idea is tame（温和的）compared to the_____（63）theories of independent geophysicist J．Marvin Herndon．Earth's inner core is made not of iron，he claims but a_____（64）of nickel and si icon Hemdon has a truly revolutionary notion：Within the nickel silicide（硅化物）inner core is also an“inner”inner core—an 8 km—wide ball of the element uranium．Uranium is radioactive．Hemdon thinks the uranium releases heat energy as its atoms_____（65）fission-split and crash into another in a chain reaction. In other words,we may live on top of a gigantic, “natural”nuclear power plant. 　　　　　　　　　
　　51 A try
　　B leave
　　C turn
　　D point
　　52 A create
　　B receive
　　C feel
　　D overcome
　　53 A work
　　B solution
　　C job
　　D patterns
　　54 A whether
　　B what
　　C why
　　D how
　　55 A from
　　B within
　　C of
　　D to
　　56 A followed
　　B dominated
　　C restored
　　D opposed
　　57 A ideas
　　B demands
　　C phenomena
　　D movements
　　58 A things
　　B acts
　　C methods
　　D records
　　59 A taken
　　B benefited
　　C left
　　D kept
　　60 A after
　　B before
　　C since
　　D when
　　61 A expanded
　　B modified
　　C gained
　　D melted
　　62 A size
　　B origin
　　C structure
　　D shape
　　63 A radical
　　B traditional
　　C classical
　　D conventional
　　64 A system
　　B copy
　　C model
　　D compound
　　65 A charge
　　B last
　　C experience
　　D show
　　 参考答案
　　51 c turn to other evidence：寻求其他证据。Tum to属固定搭配。
　　52 A create jolts：造成震动。其他几个选项意思不符。
　　53 D wayes'patterns：波浪的形状。科学家通过研究震波的形状了解地球的情况。
　　54 B 此处的意思是地心是由什么构成的难倒了她。这里应使用what构成名词性从旬，作主语。
　　55 c compose of：由……组成。固定短语。
　　56 B dominate：占统治地位，支配。Lehamann的发现在传统地球科学领域占统治地位。
　　57 A 此处的意思是：现在的科学家正用新的、激进的观点挑战传统的理论。本题只有填ideas才符合本句的意思。
　　58 D 此处填records，本句的意思是：通过分析数十万次地震波的记录，他们认为……。其他几个选项与句意不符。
　　59 c left：留下来的。此处的意思是：这一球体可能是地球形成时留下来的最古老的化石。
　　60 A 依据上下文，应用afte~句子意思才讲得通。
　　61 c gain：获取。gained mass as the planet cooled：在星球（这里指地球）变冷的过程中，它逐渐获得了质量。
　　62 B 本文主要谈地球起源问题，故此处应填ongm.
　　63 A 本句前面出现的一个词是“tame”，与之对应，应该是“radical”。
　　64 D nickel和silicon的混合物，compound：混合物。
　　65 c fission—split：裂变。经历裂变，用动词experience.